Enhancing carbon dioxide separation from natural gas in dynamic adsorption by a new type of bimetallic MOF; MIL-101(Cr-Al)

This study explores the use of a high surface area nano-adsorbent for selective adsorption and separation of very low concentrations of carbon dioxide from methane. The adsorbent, MIL-101(Cr-Al) with unsaturated metal sites, was prepared by one pot facile hydrothermal method and it was compared with MIL-101(Cr). Characterizations of the synthesized samples were conducted using XRD, FESEM, EDAX, elemental mapping, and BET analyses. Static adsorption experiments were carried out at pressures ranging from close to 1 bar up to 50 bar and at temperatures of 25 and 35 degrees C. The ideal selectivity of carbon dioxide relative to methane and the isosteric heat of adsorption were also calculated. Results indicated that with the bimetallic modification method, the CO2/CH4 selectivity increased from 5.2 to 5.7 at the pressure of 1 bar and from 8.2 to 8.3 at the pressure of 50 bar and temperature of 35 degrees C. Dynamic adsorption experiments were conducted for the mixture of CH4, CO2 and He (85 %-5% -10 % mol%). The dynamic selectivity of CO2/CH4 at the pressure of 15 bar with the space time of 1.12 min was increased from 1.82 to 4.2 using bimetallic MIL-101(Cr-Al).